1. Field of the Invention
The present invention relates to a method of selectively adsorbing CO in a gas mixture containing at least CO and CO.sub.2 with an adsorbent and separating the adsorbed CO.
2. Description of the Prior Art
The gas mixture as mentioned above includes natural gases, modified gases such as naphtha, gasified gases of coal, coke or heavy oil, gases byproduced in iron and steel works, especially shaft furnace gas and converter gas, and gases byproduced at oil refineries or petrochemical plants.
As a method for separating, concentrating or removing CO from such a gas mixture and for manufacturing an industrially usable gas, the pressure swing adsorption method (to be referred to as the PSA method hereinafter) using a solid adsorbent is known. In the PSA method, after an adsorbing component is adsorbed in an adsorbent under a pressure of normally 1 to 5 kg/cm.sup.2.G, the adsorbed component is desorbed from the adsorbent at a reduced pressure of 20 to 100 Torr. A gas booster is arranged at a location upstream from the location for performing this process.
Currently used adsorbents generally have a larger affinity for CO.sub.2 than for CO and require some pretreatment in order to separate CO from a gas mixture containing CO.sub.2. For example, in the technique disclosed in Japanese Patent Disclosure No. 59-22625, the PSA method consists of two steps of a pretreatment for removing water and CO.sub.2 and a PSA step for adsorbing CO. In a technique disclosed in Japanese Patent Disclosure No. 59-26121 for separating CO from a converter gas, mordenite is used as an adsorbent and the PSA method also consists of a PSA step of adsorbing/separating CO.sub.2 and a PSA step of adsorbing/separating CO.
However, such a two-step method requires a bulky apparatus and complex procedures.
The use of activated carbon, silica gel, activated alumina or zeolite as an adsorbent is being studied. For example, Japanese Patent Disclosure No. 58-156517 discloses a solid adsorbent consisting of halogenated Cu(I) and activated carbon as a CO adsorbent. However, no report is available which discloses that this solid adsorbent exhibits a stable, acceptable performance over a long period of time. U.S. Pat. No. 4,019,879 discloses an adsorbent consisting of a zeolite having a silica to alumina ratio as high as 20 to 200 and carrying Cu(I) thereon. However, in a zeolite having such a high silica to alumina ratio, the number of ion-exchangeable cations is generally considered to decrease. This means that the CO adsorption capacity per unit weight of the adsorbent is decreased.